This invention relates to a thread supply device for textile machines, comprising a drum on which the thread issuing from a supply bobbin can be wound tangentially and withdrawn over the end either by rotation of the drum or, in the case of a stationary drum, by means of a disc-shaped or ring-shaped winding element rotating adjacent a free front drum rim while forming at least one thread winding such that the thread is withdrawn over a removal edge of the drum in the case of a rotating drum and over a sliding edge of the winding element in the case of a stationary drum, and that a thread control element is provided which is arranged stationary adjacent the removal edge in the case of a rotating drum and which serves as a lateral stop for the unwinding thread opposite the direction of movement of the removal edge, and which is located on the winding element adjacent the sliding edge in the case of a stationary drum and which limits the peripheral velocity of the thread unwinding about the sliding edge to the peripheral speed thereof.
A thread supply device of this type is already known from German laid-open print DT-OS 2,312,267 with a rotating drum and from German laid-open print DT-OS 2,345,986 having a stationary drum. In both cases the thread control element prevents the thread removal speed from exceeding the unwinding speed as the thread is unwound from the drum in the direction of the drum axis. Since an off-the-end removal of the thread from the drum is normally used in the case of an intermittent thread supply, the thread control element ensures that a device which is suitable per se for intermittent thread supply can be employed for strictly positive thread supply.
The supply of thread is especially problematical in the case of small-scale jacquard machines. A strict positive thread supply is not expedient for such machines because the thread consumption varies within each repetition of the pattern. For this reason it was hitherto common to use an intermittent thread supply in these machines, but this is not ideal either because the amount of thread consumed for each repetition of the pattern cannot be held constant as would be desired.
The object of the present invention is therefore to develop a thread supply device of the type stated at the outset in which the thread is removed from the drum over the end similar to an intermittent thread supply device, but whose speed of removal is limited to the unwinding speed by a thread control element which laterally engages the unwinding thread in such a manner that in the case of small jacquard machines the amount of thread available to the machine is maintained respectively at a constant level through the repetition of the pattern, but in which fluctuations of thread consumption are possible in narrow limits within the repetition in order to form the pattern.
In accordance with the invention this object is accomplished in that order to use the thread supply device in small jacquard machines, a brake means acting progressively on the unwinding thread in the peripheral direction of the same is disposed in front of the thread control element in the sense of the thread rotating about the removal or sliding edge during the thread removal such that the braking effect is amplified as the thread approaches the thread control element and is decreased as it moves away from the thread control element.
In the case of the thread supply device in accordance with the invention, the maximum amount of thread per unit time which the knitting machine can take up is limited by the thread control element to that amount of thread which is wound on the drum per unit time. In this way the amount of thread consumed per repetition of pattern cannot exceed a specific maximum limit in any case. The thread supply device in accordance with the invention is normally operated on small jacquard machines, however, such that the thread is removed from the drum with a certain amount of angular spacing from the thread control element. If the thread consumption increases, it can approach the thread control element somewhat against the increasing resistance of the braking device, whereas it moves away from the thread control element in the direction of winding with a reduction of the braking effect if the thread consumption decreases. The thread consumption can thus vary somewhat about an average value, these fluctuations being dampened by the increasing and decreasing braking effect and is limited on the one hand by the control element and on the other hand by a common switch-off means if it exceeds the permissible limit. The thread control device in accordance with the invention is thus an intermediate between a purely positive and a purely intermittent thread control device which permits the thread requirements which fluctuate over the small pattern within narrow limits to be met in small jacquard machines, but to strictly limit the amount of thread to a maximum amount over the repetition of pattern.
It is provided in the preferred embodiment of the invention that the brake means have a constant braking effect over an operation angle section of the thread rotation, and that the braking effect increase from the operating angle section toward the thread control element and decrease away from said thread control element. This ensures that in that area in which the thread is noramlly withdrawn from the drum a constant thread tension is exerted on the thread. The braking effect is increased or decreased only when the thread attempts to mvoe out of this normal operating area in order to compensate in this manner for undesired large fluctuation in thread consumption or thread tension.
The brake means is expediently a curved guide part over which the thread passes and is deflected farther out of its path the closer it approaches the thread control element in the direction of thread rotation about the removal or sliding edge during thread removal. The braking effect is achieved in this case with simple structural means by a greater or lesser deflection of the thread out of its path and by corresponding greater or lesser friction exerted on the curved guide part. This is simpler than if another type of brake means were provided, e.g. a spring-action rotatably supported guide arm supporting a guide eye for the thread, although the latter would also be possible.
An especially simple structural design results if the curved guide part is a loop-shaped wire bracket positioned adjacent the removal or sliding edge, through whole interior the unwinding thread passes and which extends the more radially within the removal or sliding edge over its entire effective area the more it approaches the thread control element in the direction of thread rotation about the removal or sliding edge during thread removal. The brake means in this case is a simple wire bracket along whose peripheral the measure of thread deflection and thus the braking effect is varied without any additional structural means by making its radial spacing from the removal or sliding edge greater or smaller.
In the preferred embodiment of the invention, it is provided that the wire bracket has the shaped of a closed loop which forms a stop section forming the thread control element and extending radially relative to the removal or sliding edge and a first brake section connected thereto contrary to the direction of thread rotation during thread removal and having a radial spacing relative to the removal or sliding edge which is reduced as the distance from the stop section increases, an operating section with a constant radial spacing from the removal or sliding edge and a second brake section with a radial spacing from the removal or sliding edge which decreases even further as the distance from the stop section increases, a shut-off section extending externally of the removal or sliding edge and a connecting section between the shut-off and stop sections which is not contacted by the thread in any normally occuring operational phase. In this case, all control functions which affect the thread after its removal from the drum are combined on a simple, loop-shaped wire bracket. The stop section forms the control element which limits the speed of removal to the unwinding speed. Two brake sections extend on both sides of an operational section which the thread passes during normal operation with a constant radial spacing from the removal or sliding edge, a switch-off section being connected to the one brake section. This functions simply in that the braking effect is completely neutralized by reducing the radial spacing of the wire bracket relative to the removal or sliding edge to zero or to a negative value so that a conventional shut-off device can bring the the thread supply device or the textile machine to a standstill. Hence, all control functions are met in this case using the simplest structural means.